Genetic Algorithm(GA) is an optimization algorithm based on the biological evolution and is known to be suitable for multi-disciplinary design optimizations because of the global searching ability. However, slow convergence and high computational cost can make the applicable range of CA limited to rather simple problems. In the case of airfoil designs, it. is restricted within 2 dimensional inviscid designs at present. In this paper, aerodynamics and RCS coupled design optimization is performed using a genetic algorithm. To resolve the problems such as convergence and computational cost, a hybrid GA is designed. For an, aerodynamics and RCS coupled design, not only 2D inviscid analysis but also viscous analysis are applied as aerodynamic analyses and RCS analysis is applied for the high frequency region, not for the low frequency region as was usually done.